Cryogenic cooling systems

ABSTRACT

1208751 Refrigerating BRITISH OXYGEN CO Ltd 4 Jan 1968 [5 Jan 1967] 727/67 Headings FIR R3AD4X R94 and R3A3D10 A conduit supplying a mixture of gas and liquefied gas to a load to cool it is surrounded by a sheath of gas passing from the load. As illustrated, liquid nitrogen in a container 1 is forced by the pressure of nitrogen in the space 26 into a transfer conduit 3 connected to an infrared detector 11  which is to be cooled. Gas from the detector 11 passes through a duct 5 surrounding the conduit 3  to an exhaust valve 55 which is used to control the flow-rate of liquid to the detector. The liquid nitrogen is partially vaporized in the conduit 3 by heat-transfer through the conduit well and is fully vaporized by the heat generated by the detector. The transfer conduit is made of polyvinylchloride and has an internal diameter of between &lt;SP&gt;1&lt;/SP&gt;/ 16 th and &lt;SP&gt;5&lt;/SP&gt;/ 16 th of an inch. The container 1 is connected by conduits 21 and 25 to a valve mechanism 7. In the illustrated position of the latter, the conduit 21 is closed by a valve-member 35 and the conduit 25 communicates with the atmosphere through a pressure relief valve 47 which is set to maintain a pressure of between 1 and 3 p.s.i.g. in the nitrogen gas space 26. In order to fill the container 1, a filling pipe is connected to an inlet port 17 thereby raising an actuating member 31 which in turn raises valve-members 42 and 35 to allow communication between the conduit 25 and an exhaust 27 to atmosphere and between the conduit 21 and the filling pipe. Instead of nitrogen, the system may use oxygen, argon or hydrogen.

Jan. 27, 1970 l T. HlGGs ETAL 3,491,542

CRYOGENIC COOLING SYSTEMS Filed Jan. 2. 1968 Mft/ENTORS United States Patent O 7 Int. Cl. F17c 7/02; F25d 21/04 U.S. Cl. 62-45 4 Claims ABSTRACT F THE DISCLOSURE In a system for cooling a heat-dissipating load by means of a cryogenic fluid passed through a transfer conduit to the load in the form of a two-phase liquid/ gas mixture, frost or ice formation on the conduit is inhibited by shrouding the conduit with a stream of dry gas exhausted from the load.

-Field of the invention This invention relates to cooling systems employing a cryogenic uid as coolant, and in particular to such systems in which the cryogenic fluid is supplied to a region to be-cooled as a two-phase mixture of liquid and gas.

Description of the prior art In some applications, such as when cooling infra-red detectors used with aerial reconnaissance and guidance systems, the required flow rate of coolant is less than that which is readily obtainable from a continuous stream of cryogenic liquid. It has been proposed to'employ a twophase mixture of liquid and gas as coolant to achieve the required low iiow rate. The two-phase mixture is produced by passing cryogenic liquid from a source to a region to be cooled along a transfer conduit which is exposed to the surrounding atmosphere to permit heat to flow into the conduit so as to vaporise part of the cryogenic mixture and produce a -gas stream in which globules of cryogenic liquid are suspended.

Such a two-phase cooling system functions satisfactorily for short periods of time but it has been found on pro-` longed runs that the system suffers from the disadvantage that moisture from the surrounding atmosphere condenses on the conduit, particularly on that part of the conduit adjacent the cryogenic liquid source, leading to the formation of frost or ice on the conduit and forming a thermally-insulating layer which interferes with, and ultimately stops, the vapourisation of the liquid to form the gas phase.

Summary of the invention The formation of frost or ice on the surface of a transfer conduit carrying a two-phase (liquid/ gas) mixture of a cryogenic fluid is inhibited by shrouding the conduit with a stream of dry gas from the load being cooled.

Accordingly the present invention provides a cooling system employing a cryogenic fluid which, in its broadest aspect, is as defined in the appended claims.

According to another aspect of the present invention there is provided a method of cooling a region to be cool-ed which, in its broadest aspect, is as defined in the appended claims.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing which shows a side elevation, in section, of a diagrammatic cooling system of the invention and as used for cooling an infra-red detector.

Referring to the drawing, the cooling system shown comprises a container 1 of liquid nitrogen, a transfer conduit 3 having a spaced outer jacket 5, and a valve 7 ICC (shown on an enlarged scale) through which the container 1 may be lilled and by Iwhich the container may be pressurised to force liquid nitrogen v9 along the transfer conduit 3 to an infra-red detector shown diagrammatically at 11.

The valve 7 comprises a lower compartment 13, a middle compartment 15 and an upper compartment 16 which are axially aligned. The lower compartment 13 has an axial inlet port 17 to which a nitrogen supply line (not shown) may be coupled, and a radial outlet port 19 connected by a delivery conduit 21 to the lower part of the container 1. The middle compartment 15 has a radial outlet port 27, and it is able to be placed in communication with compartment 16 by movement of a valve member 42 cooperating with a valve seat 41. Compartment 16 has an inlet port 23 connected by a conduit 25 to the gas-lled space 26 above the liquid nitrogen 9 in container 1. l

The inlet port 17 and the outer port 19 of the lower compartment 13 are separated by a valve seat 29 having a central aperture 30 through which extends an actuating member 31 having an enlarged diameter part 33 projecting into the inlet port 17. A valve element 35 surrounds and is an easy fit on, the actuating member 31 and is biassed towards the valve seat 29 by a resilient bellows unit 37 attached at one end to the stem of actuating member 31.

The actuating member extends into the middle compartment 15 through a central aperture 38 in the wall 39 separating the two compartments, and is a sliding fit within the aperture 38. The valve seat 41 separates the inlet 23 from the outlet port 27. In compartment 16 is a valve element 42 which is movable with member 31, which is biassed downwardly as viewed in the drawing by a spring 43. That part of member 31 which extends into the compartment 15 is coupled to the wall 39 by a second bellows unit 45 to provide a gas-tight seal between compartments 13 and 15.

A recess 46 formed in the upper wall of the compartment 16 communicates with a pressure-relief valve 47 and a pressure gauge 48 and is isolated from the compartment 16 by the valve element 42 which seats against the upper wall of the compartment when the actuating member 31 is moved to its fully-raised position.

As previsously described the valve 7 is connected to the container 1 by the conduits 21 and 25. In the drawing the container 1 is shown partially filled with liquid nitrogen 9, and has an outer vacuum-insulated vessel 51. The transfer conduit 3 extends from the base of the container 1 out through the container and outer vessel 51 to the infrared detector 11. Between the outer vessel 51 and the detector 11, the transfer conduit 3 is surrounded by a jacket 5, the jacket adjacent the outer vessel 51 having an enlarged end portion 6 which accommodates the curved portion of the conduit 3. The jacket 5 is connected to the neck of the detector 11 and provides a return path for gas from the detector 11, the gas owing through the jacket 5, a tube 53 connected to the jacket, and to the atmosphere through a control valve 55.

To achieve a two-phase flow of coolant, the internal diameter of the transfer conduit 3 is preferably between inch and 5/6 inch. If the internal diameter is less than about 1/16 inch it has been found that the liquid nitrogen is completely vaporised in passing along the conduit, while if the internal diameter is greater than E/16 inch the globules tend to deposit from the stream and interrupt the two-phase ow. In the described embodiment, the generally-horizontal part of the transfer conduit 3 extending between the end portion 6 of the jacket 5 and the detector 11 was formed from polyvinylchloride tubing, while the remainder of the conduit was formed from stainless steel tubing. A suitable length for the transfer conduit was 6-12 feet. Other suitable materials may be used for form- 3 ing the transfer conduit 3, but to achieve two-phase flow a smooth borefis required. ,Y

To charge the container 1 with liquidnitrogen, a coupling (not shown) from a reservoir of liquid nitrogen is connected tothe inlet port 17. In so doing thegcoupling contacts the actuating member 31 and moves it against thebias of spring 43Y so that when the coupling is fullyengaged, the actuating member 31 is ina fully-raised position with yalve elements 3? and 42Y lifted from valve seats 29 and 41 respectively, and with valve element i2 in contact with the upper wall of compartment 16 to islate the remaindereof this compartment from recess 46. Liquid nitrogen is then fed through the iniet port 17, outlet port 19, and delivery conduit 21 to the container n1, displaced gas being vented to atmosphere fromihe VAtop of container 1 through the conduit 25, Yinlet port 23 and outlet port 27. When sufficient liquid has been fed to the container 1, the coupling isdisconnected from the inlet port 17, during which operation the actuating member is returned to the position shown in the drawing by the action of spring 43, therebyisolatingrthe conduit 21 from the inletport 17; isolating conduit 25 from the outlet port 27, and connecting: conduitl25 to the vent valve 47 and VJpressure gauge 48.

The vent valve 47 is arranged to open at a :pressure with the range of l3 p.s.i.g.,.which isrthe pressure required for forcing nitrogen as a two-phase mixture along the conduit 3. This pressure will be quickly reached after filling the container 1 and the cooling operation is begun bygopening the flow control valve 55 by the required amount. ,Y i n When the cooling system Vis operating liquid nitrogen is passed into the transfer conduit under the pressure applied to the surface of the liquid nitrogen 9 Yin the container 1. in the portion of the conduit 3 surrounded by the jacket 5 part of the liquid is vaporised byheat passing Ythroughgthe conduit wall from the surrounding-atmosphere to produce a two-phase mixture of liguid and gas.

The two-phase mixture is delivered Yto the infra-red detector 11 which is thereby cooled to liquid nitrogen temperatures. In detector 11 virtually the whole of the liquid phase is converted to the gas phase, and the gas phase from the detector 11 is fed through the jacket 5 to atmosphere via the flow control Avalve 55. The flow rate of the two-phase coolant is adjusted by the valve 55, a suitable rate being 750 cc./min. nitrogen gas to cool an infra-red detector of 0-.5 watt load to the temperature of liquid nitrogen.

It will be seen that because the gas which shrouds the conduit 3 is obtained solely from the liquid nitrogen, a moisture-free atmosphere surrounds the conduit 3, and frost or ice formation on the conduit is thereby avoided. It has been found that the temperature difference between the shrouding gas obtained from the detector 11 and the conduit is suicient for there to be sufficient heat transmitted through the wall of the conduit to maintainthe ow of coolant in its two-phase state. Using a 3.5 litre liquid nitrogen container, the cooling system has been fund to operate satisfactorily for periods of up to 16 hours.

It will be apparent that, depending upon the application, cryogenic liquids other than liquid nitrogen may be employed asY the source of coolant, for example liquid oxygen, liquid argon and liquid hydrogen.

We claim: l 'i i A cooling system employing a :cryogenic tluid, including a thermalhJ-inSuIatel container for liquid cryogenic fluid; a transfer cond-uit having one end dipping below the minimum level of liquid in the container and having itsi other end connected to a heat-dissipating load, the conduit being so .constructed asto transmit sufficient heat through its walls to vaporise some of the liquid ow- :ing along it to form a two-phase mixture of liquidrand gas; means for causing the liquid fiow fromrthe container through the transfer conduit towards the load, and a jacket enclosing at least that part of the transfer conduit which is adjacent to thel container, the jacket being connectedat one end to the load to receive the gas phase of the cryogenic fluid so that that said partfof the transfer conduit is shrouded from the atmosphere by a stream of drygas.

2. The cooling system claimed in Iclaim 1, in which the jacket is in communication with the atmosphere through a control valve at that end which is reniote from the said load.

3i The cooling system claimed in claim 1, in gwhich the container has connected to it two additional conduits, one being for the delivery of liquid cryogenic fluid and the other being for the exhaust of gaseous cryogenic fluid.

4. The method of transferring .cryogenic liquid through aY conduit connecting a supply souree of theliquid with apparatus in which the liquid is vaporised by heat for the performance of work, which comprises: causing the liquid to ow from the supply source into the apparatus; discharging the gas generated in the apparatus by passing it to atmosphere as a confined stream shielding and surrounding the liquid transfer conduit in heat exchange relation therewith; vaporising a portion of the liquid in the transfer conduit by heat derived solely from the surrounding exhaust gas stream; and selectively regulating the flow rate of discharge of the shielding gas tothe atmosphere whereby to correspondingly regulate the extent of liquid vaporisation in the transfer conduit.

References Cited UNITED STATES PATENTS 2,913,609 11/1959 Lennard 62-514 2,964,919 12/1960 Howlett 62-55 3,006,157 10/1961 Haettinger et al 62--514 3,055,191 9/1962 Dennis 62-514 3,302,419 2/1967 Walter 62-514 LLOYD L. KING, Primary Examiner Us. ci. x.a, isz- 55, 514 

